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  #1  
Old 07-27-2020, 04:46 PM
swjohnsey swjohnsey is offline
 
Join Date: Nov 2018
Location: Kingsville, TX
Posts: 241
Default Downside of taking off with flaps?

I followed a couple of threads about taking off using flaps. I experimented with my RV-4 using flaps aligned with fully deflected aileron (15degrees?). I get noticeable shorter take-off run. Is there a down side?

I normally let it fly off at 65 mph and accelerate in ground effect to 100mph before climbing out at 120mph. With flaps I was coming off at 55 and accelerating to around 80 in ground effect before bring the flaps up and continuing in ground effect 'til 100 then climbing out at 120.

This is a RV-4, IO360 with Hertzel CS.
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  #2  
Old 07-27-2020, 04:56 PM
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Mel Mel is offline
 
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The only down side to taking off with flaps is forgetting to raise them.
One of the reasons I always do it is it becomes part of the routine.
I have an indicator light on my boost pump for the same reason. Once I have established climb and cleared obstacles, the boost pump is off and the flaps are up.
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  #3  
Old 07-27-2020, 04:58 PM
Ralph Inkster Ralph Inkster is offline
 
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Generally I don't bother with take off flaps. A few times it has come in handy to pop off the runway if taking off in heavy or long grass, but suck them up as soon as possible to prevent heating up the engine during the climb out.
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  #4  
Old 07-27-2020, 05:11 PM
BobTurner BobTurner is offline
 
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Location: Livermore, CA
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As Mel says, you need to remember to raise them promptly. RVs accelerate so well that it’s easy to blow right thru max flap speed before they’re retracted - even more so with this ‘accelerate in ground effect’ method.
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  #5  
Old 07-27-2020, 05:18 PM
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Ironflight Ironflight is offline
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Location: Dayton, NV
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Quote:
Originally Posted by Mel View Post
The only down side to taking off with flaps is forgetting to raise them.
One of the reasons I always do it is it becomes part of the routine.
I have an indicator light on my boost pump for the same reason. Once I have established climb and cleared obstacles, the boost pump is off and the flaps are up.
But Mel, did you have a gear over speed horn On the -6 in case you forgot and left the gear down?!
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  #6  
Old 07-27-2020, 05:36 PM
DeltaRomeo DeltaRomeo is offline
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Short grass field with obst. at the end might be the perfect Vx use of Flaps 1.

On day one of Phenom initial the instructor said, "Of the five of you in here, three of you will overspeed the flaps on your first sim takeoff." He was right. And the RV speeds up plenty fast too.

99% of the time I'm Flaps 0 on RV takeoffs, but there's an after takeoff checklist to remind me just in case. Yes, I've forgotten <g>
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Last edited by DeltaRomeo : 07-27-2020 at 05:49 PM.
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  #7  
Old 07-27-2020, 05:38 PM
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Mel Mel is offline
 
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Quote:
Originally Posted by Ironflight View Post
But Mel, did you have a gear over speed horn On the -6 in case you forgot and left the gear down?!
MAX gear-down speed is VNE! If you over speed that, the landing gear is NOT your number 1 priority.
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  #8  
Old 07-27-2020, 05:54 PM
gereed75 gereed75 is offline
 
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This is probably one of those things that for every pro there is a con.

I personally never use them on TO. Part of my reasoning is safety - if engine fails, I do not want the drag. Yes I want them down to land, but remembering to get them down is probably way more likely to happen in extremis than remembering to retract them in extremis.

Additionally I want all of the energy on the airplane I can get during take off, as soon as I can get it. The more energy I have during the early climb out phase In case of an engine failure, the more energy I will have to deal with the options

Where would you rather be 250’ off the ground as the runway goes behind you with a dead engine; with a clean airplane with 100 knots looking at places to go, or retracting the flaps at 85 knots grabbing your arse?.

Again, probably lots of pros and cons, but personally I would rather be through this critical phase of flight as quickly as possible.
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  #9  
Old 07-27-2020, 07:08 PM
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Mel Mel is offline
 
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Quote:
Originally Posted by gereed75 View Post
This is probably one of those things that for every pro there is a con.
I personally never use them on TO. Part of my reasoning is safety - if engine fails, I do not want the drag. Yes I want them down to land, but remembering to get them down is probably way more likely to happen in extremis than remembering to retract them in extremis.
Additionally I want all of the energy on the airplane I can get during take off, as soon as I can get it. The more energy I have during the early climb out phase In case of an engine failure, the more energy I will have to deal with the options
Where would you rather be 250’ off the ground as the runway goes behind you with a dead engine; with a clean airplane with 100 knots looking at places to go, or retracting the flaps at 85 knots grabbing your arse?.
Again, probably lots of pros and cons, but personally I would rather be through this critical phase of flight as quickly as possible.
Flaps are not only for drag. They also produce lift. Why do you think airliners use flaps for take off? On the RV series of aircraft the range of 15° flap is pretty close to best L/D. At this point you are producing more lift than drag.

With proper use of flaps, you will be at a higher altitude when your failure occurs.
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EAA Flight Advisor/Tech Counselor, Friend of the RV-1
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RV-6 Flying since 1993 (sold)
<rvmel(at)icloud.com>

Last edited by Mel : 07-27-2020 at 07:26 PM.
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  #10  
Old 07-27-2020, 07:35 PM
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Ed_Wischmeyer Ed_Wischmeyer is offline
 
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Don't know about the other nosedraggers, but on the RV-9A on a narrow runway, takeoff with no flaps can make the runway disappear. I always take off with flaps 10 for just that reason, and so that I'm always expecting the same thing.

I also practice instrument go-arounds, and use the same litany on takeoff: full power, 80 knots, flaps up. I leave takeoff power in for a bit to accumulate energy in case the engine goes poop, but if I waited till power reduction to retract the flaps, I bet I'd overspeed them. And with the constant speed prop, the -9A accelerates so quickly that there's little concern for the plane settling with flap retraction.
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